If the Frenchmen excel them (Germans) in vivacity of onslaught,
if the Englishmen are their superiors in toughness of resistance,
the Germans excel all other European nations in that general
fitness for military duty which makes them good soldiers under
all circumstances.

Glory Years of the Prussian Army.
Frederick the Great imposed so spartan discipline
that 400 officers "are said to have asked to resign".

In 1740s Prussia owned 85.000 troops which gave her the 4th largest army in Europe, even though her lands stood at 10th in order of size and only 13th in population !
It means that it was possible for an agricultural state of few millions of inhabitants, on a small territory, without a fleet or direct maritime commerce, and with comparatively little manufacturing industry, to maintain, in some respects, the position of a great European power.
Truly amazing.
Frederick had devised Europe's first-ever battle-scale maneuvers in 1743, which gave his generals invaluable peacetime experience in directing large scale bodies of troops."
(Duffy - "Instrument of War" Vol I p 117)

The Prussian, as well as the German in general, makes capital stuff for a soldier.
They are, withal, among the most pugnacious people in the world, enjoying war for its own sake, and often enough going to look for it abroad, when they cannot have it at home.
From the Landsknechte of the middle age to the present foreign legions of France and England, the Germans have always furnished the great mass of those mercenaries who fight for the sake of fighting.
"If the French excel them in agility and vivacity of onslaught, if the English are their superiors in toughness of resistance, the Germans certainly excel all other European nations in that general fitness for military duty which makes them good soldiers under all circumstances." (Source: "The Armies of Europe" in Putnam's Monthly, No. XXXII, publ. in 1855)The Prussian army was made up of Germans and also Poles from Silesia, Posen, Pomerania and eastern Prussia. (After the partitions of Kingdom of Poland, Prussia acquired large territory in the east. The greater part of these lands have been germanized by sales and grants of public domains to Prussian colonists and by measures against the Polish inhabitants.)

Foreign generals and observers admired the Prussian military machine of 18th Century. Austrian commander, Prince Eugene of Savoy, reported that "the Prussian troops are the best of the German forces. The rest are pretty well useless."
The Prussian army enjoyed reputation as one of the best trained, the most disciplined and one of the best led (Frederick the Great, Zieten, Seydlitz and other generals). They wore simpler dress than the French army with its many lackeys, cooks, courtesans, actors and chaplains, friseurs and valets, chests full of perfumes, hair nets, sun shades and parrots. Frederick the Great imposed so spartan discipline that 400 officers "are said to have asked to resign". Frederick's troops fought with great success against the Russians, French, Germans, Swedes and Austrians.

The Prussians could march off to the battlefield in perfect order in a holy silence. The state of affairs which prevailed in the French army was somehow different, there was a near riot when even the small troop had to turn out. So this is not surprising that France had suffered a certain loss of prestige through her shocking defeats in the war against Frederick's army.

The Prussian infantry was magnificent, marching in calm and silent lines under a withering fire. They moved doggedly forward until the enemy began to mass in terrified flocks around their colors. When the drums were playing "Ich bin ja Herr in deiner Macht !" it made a massive impression on everyone. One eyewitness wrote "I have never been able to hear that melody without the deepest emotion." The best part of the army however was the cavalry. One dragoon regiment routed 20 battalions and captured 66 colors ! In 1745 at Soor 26 Prussian squadrons routed 45 enemy squadrons deployed on a hilltop. Only the engineers and artillery were the weak link of Frederick's army.

King Frederick the Great, used the army to enter upon a period of conquest. In 1740 on a
slim pretext and without a declaration of war, he invaded Austrian territory.

.

.

.

1757 Battle of Leuthen:
It was a decisive victory for Frederick the Great that ensured his control over Silesia. This is important battle from military point of view as Frederick used Oblique Order.
This is a tactic where an attacking army refocuses its forces to attack enemy flank. The commander would intentionally weaken one portion of the line to concentrate their troops elsewhere. They would then create an angled or oblique formation, refuse the weakened flank and attack the strongest flank of the enemy with a concentration of force. First recorded use of the tactic similar to oblique order was at the Battle of Leuctra, when the Thebans defeated the Spartans (ext.link). This tactics required disciplined and well trained troops able to execute complex maneuvers.

Frederick the Great was succeeded by Frederick Wilhelm II. Under his rule Prussia became even larger by the partitions of Poland of 1793 and 1795 but also underwent a period of eclipse.
The failure to reform and the lack of preparedness after the death of Frederick the Great in 1786,
and the real efficiency in the field was sacrificed to precision on the parade-ground led to the decline of the army.
Defeated by the French Revolutionary army, Prussia withdrew from the coalition and remained neutral until 1806. Then her armies were crushed by Napoleon at Jena and Auerstedt. In 1807 Prussia had to accept the harsh Treaty of Tilsit, by which it lost most of its share of Poland and became a virtual dependency of France.

"... just after the victories of Jena and Auerstadt, in which Napoleon destroyed the Prussian army and shook the Prussian state to its core, was to be something of a turning point. The Prussians were shocked and insulted by the French victories, but they also saw them as proof of the superiority of France and her political culture. When Napoleon rode into Berlin he was greeted by crowds which, according to one French officer, were as enthusiastic as those that had welcomed him in Paris on his triumphant return from Austerlitz the previous year. 'An undefinable feeling, a mixture of pain, admiration and curiosity agitated the crowds which pressed forward as he passed,' in the words of one
eyewitness...
But he treated Prussia and her King worse than he had treated any conquered country before. At Tilsit he publicly humiliated Frederick by refusing to negotiate with him, and by treatening Queen Louise, who had come in person to plead her country's cause, with insulting gallantry. He did not bother to negotiate, merely summoning the Prussian Minister Goltz to let him know his intentions. He told the Minister that he had thought of giving the throne of Prussia to his own brother Jerome, but out of regard for Tzar Alexander, who had begged him to spare Frederick, he had graciously decided to leave him in possession of it. But he diminished his realm by taking away most of the territory seized by Prussia from Poland ... " (Zamoyski - "Moscow 1812" p 43)

US Army military staff service has
its origins in the Prussian army.
In the the US Staff College Publication 1
is clearly stated that "The modern general
staff was developed in Prussia during
the XIXth century."

Despite small population (see diagram below) Prussia had the fourth largest army in the world.
Such army required an efficient staff. The origins of what would become the German General Staff of the 19th and 20th Centuries - probably the most professional military machine in the world - can be traced to the Prussian Army of the French Revolutionary and Napoleonic Wars.

The chief-of-staff was on army, corps and brigade level. Each of the had a goup of staff officers. In 1809 a corps of permanent staff officers was established and specific uniforms were introduced for them. The role of chief-of-staff on the three levels (army, corps, brigade) explained Peter Hofschroer and Mark Adkin:Chief-of-staff of Army

The supreme command was naturally the responsibility of the army's commanding general, with the role of his chief-of-staff [of the army] being to turn the commanding general's intentions into practical plans. "The Prussian General Staff operated under a chief-of-staff system. In this instance Lieutenant-General von Gneisenau filled the post officially known as Quartermaster-General. He was the second-in-command to Blücher, as well as being responsible for co-ordinating all staff functions. He was also the officer representing the Minister of War with the army, and had juridiction (under the commander who took overall credit or blame for the army's activities) over both operational and administrative matters.
In the field Gneisenau wielded his authority in the name of the commander-in-chief in virtually all military spheres - movement, tactics, deployment, intelligence and logistics (food, clothing, ammunition and accommodation). Blücher made the major decisions after consultation with Gneisenau and others, such as Major-General von Grolmann who headed the staff at the headquarters."
(Adkin - "The Waterloo Companion" p 111)
Chief-of-staff of Corps

"The chief-of-staff of a corps was responsible for its organisation and leadership, acting as an advisor to the corps commander... Chief-of-staff of (Division) Brigade

These [brigade staff officers] dealt with matters such as the reconnaissance of terrain and any resulting changes in the direction of the marching columns ... with reconnoitring the enemy and the countryside, particularly with regard to the supply and quartering of the troops; with the receipt and implementation of orders regarding combat, deployment and marching. Finally, the brigade staff officer was required to deal with every matter drawn to his attention by the brigade commander."
(Hofschroer - "Prussian Staff..." p 11)

After Napoleon's defeat in 1815 at Waterloo by Prussian and the German-British-Netherland army, Europe entered a long period of peace. Armies were cut back and interest in military science waned in most nations. Only in Prussia did military men study the crises of command that emerged during the last stages of the Napoleonic Wars, when mass armies took to the battlefields.
If Napoleon Bonaparte was the last Great Captain of history, then von Moltke (ext.link) was the first Great Manager of the modern military era. He built up a new system based on the principle of using highly trained and interchangeable staff officers. Noting von Moltke's success over the French army, all major European nations copied his methods.

"At Jena, the Prussian army performed the finest
and most spectacular maneuvers, but I soon put
a stop to this tomfoolery and taught them that
to fight and to execute dazzling maneuvers and
wear splendid uniforms were very different matters." - Napoleon

Decline of the Army.
Defeats at Jena and Auerstadt

In 1806 the Prussian army consisted of 200,000 men: 133,000 infantrymen, 39,600 cavalrymen and 10,000 artillerymen and few thousands of engineers, garrisons, reserves etc.

Napoleon's efforts to get Prussia to close its ports to British goods in 1806 had revealed a problem. When Prussia agreed, the British navy retaliated by seizing 700 Prussian merchant ships in port or at sea and blocking their access to the North Sea. Facing economic collapse, the Prussian king then turned his anger on Napoleon, rescinding their agreements and ordering the French out. That in turn led to war, Napoleon's trouncing of the Prussian army at Jena (ext.link) and Marshal Davout at Auerstadt, and the creation of the Continental System. Napoleon's army marched into Berlin.
By the treaty of Tilsit, Prussia was reduced to the status of a second rate power. She lost territory in Westphalia, Poland and along the Elbe River.

Although the Prussian army began Napoleonic wars with a fearsome reputation it was quickly destroyed by the French.
Napoleon wrote: "When I went to see the king of Prussia (Friedrich Wilhelm III ext.link), instead of a library I found he had a large room, like an arsenal, furnished with shelves and pegs, in which were placed fifty or sixty jackets of various cuts ... He attached more importance to the cut of a dragoon or a hussar uniform than would have been necessary for the salvation of a kingdom. At Jena, his army performed the finest and most spectacular maneuvers, but I soon put a stop to this tomfoolery and taught them that to fight and to execute dazzling maneuvers and wear splendid uniforms were very different matters. If the French army had been commanded by a tailor, the king of Prussia would certainly have gained the day."
(In the following years the reformers encouraged Friedrich Wilhelm's interest in designing the new uniforms to keep him from interfering with their more radical measures.)

"The Prussian Infantry who mobilised in 1806 were products of a system that had not altered since the Seven Years' War. They were immaculately dressed, drilled into unquestioning obedience, savagely punished if they fell foul of their commanders and were unfit for the new type of warfare in every possible way. At Auerstädt and Jena, they discovered their training was totally inadequate and as Napoleon's troops tore into the retreating Prussian army, its elderly commanders succumbed to panic or shocked paralysis. The whole campaign was epitomised by the surrender of Hohenlohe's army at Prenzla, where Murat was able to bluff a vastly superior force into laying down its arms. Twenty-nine thousand men under L'Estocq managed to link up with the Russian army in East Prussia, but by the end of November 1806, the majority of the Prussian Army had surrendered and Frederick the Great's sword and sash were on their way to Les Invalides as trophies. The basic material of the old army, the private soldier, was sound, but internal weaknesses had meant that the Prussian army was out-thought as well as outfought." (Robert Mantle)

Peter Hofschroer gives three main reasons for why Prussia was defeated in 1806.

Not joining Austria and Russia in 1805 in the Third Coalition. This combination would most likely have led to Napoleon's defeat.

Going to war against France in 1806 without the direct support of another great power.
The Prussian army should have adopted a defensive strategy until the arrival of the Russians.

Dividing the army into three in the face of the enemy.
Nobody was really in charge and King Frederick William III lacked the authority to impose his will.

In 1806 Napoleon was very interested in the Prussian army.
Chlapowski writes: "... the Emperor asked me about very many things. He fired questions at me as if I was sitting an exam. He already knew from our conversations ... that I had served in the Prussian amry, so he asked about my studies there, about my military instructors, about the organization of the artillery and of the whole Prussian army, and finally he asked how many Poles were likely to be in the corps which was still in East Prussia beyond the Vistula under General Lestoq. I could not answer this question but pointed out that most of his corps must be Lithuanians, as it had been mainly recruited in Lithuania. At that time, since the last partition [of Poland] the whole district of Augustow belonged to Prussia. I also explained that in Lithuania only the gentry were Polish, and the people Lithuanians. He did not know anything about Lithuania ... The Emperor listened patiently and carefully to all these details. ... [he] asked me about the [Prussian] military academies. How far did they go in the study of mathematics ? He was surprised at the elementary level at which they stopped. Didn't they teach applied geometry ? I myself had not learned this, but only later studied it in Paris."
(Chlapowski/Simmons - "Memoirs of a Polish Lancer" p 12-13)

"The schooling of subaltern officers, of captains
and battalion commanders is exemplary and still
an object of envy and imitation by our neighbours,
but what about the schooling of generals ?
Where is the opportunity to be trained as a general,
i.e. as an independent commander of all arms ?."
- Massenbach

Reforms of 1806-1813.
Corps System and People's Army
People's Army

Digby-Smith writes: "Under the terms of the Treaty of Tilsit of 1808, Prussia's army had been limited to 42,000 men. By dint of much creative thinking, however, Scharnhorst and other members of the Prussian General Staff had invented the Krumper System by which each regiment called up a certain number of recruits, gave them basic military training, and then discharged them again in order to call up and train another batch, so that the 42,000 ceiling imposed by Napoleon was never exceeded." (Digby-Smith, - p 35)
The Prussian military did assessed how and why the disaster had occurred. The requirements included:

raising new troops

practice in the art of skirmishing

training in the divisional and corps system

accountability of the armed services to the German people

institutionalization of military genius in a centralized, elite general staff
Prussia was fortunate to possess, at this low ebb in its history, such able reformers as Gerhard von Scharnhorst and August, Graf von Gneisenau who put the Prussian army on a modern basis.

People's Army.
Scharnhorst reforms like strenuous selections of officers from a broad base of the population, gave the Prussians what they sought - professional officers and NCOs. The Prussians had to be able to mobilize very rapidly. Their officers had to "prepare hard in peacetime in order to be ready when war began."
An army during Napoleonic wars was based on one of the two systems:

the recruitment of volunteers, which is antiquated and only possible in exceptional cases such as surrounded by waters England.

or universal conscription.
The idea behind the Prussian law was that every citizen who is physically capable of bearing arms thereby has the obligation to do so personally in defence of his country, during his years of military fitness. This idea was superior to the principle of purchasing substitutes which was found in others countries having a conscriptive system. It was the Krumper System introduced by Scharnhorst. Once the young men were trained, they were then sent home and replaced by new ones. Under the noses of French spies Prussia developed a reserve army capable of taking the field. On March 1st 1813 were established so-called Reserve Battalions. They were considered as part of their parent regiments and were made of reservists and raw recruits. The officers and NCOs were supplied by the parent regiments. The 39 Reserve Battalions formed twelve Reserve Regiments. In March 1814 these units were assigned numbers in line.
Scharnhorst also persuaded King Friedrich Wilhelm III to institute a national militia called Landwehr. The Landwehr accepted men aged 25 to 40, too old and weak for the army. They were equipped not by the central goverment and ministry of war but by provinces.
So in 1813-1814 the Prussian troops were of four types: regular, reserve, volunteers and Landwehr.

Brigade (Divisional) and Corps System.
Already in September [1806] the Prussian army was organized into 14 divisions of all arms. "The ill-considered aping of the French, conducted at the last minutedid not take into account the lack of trained divisional staff to command these formations... The few officers of the QGS [Quartermaster General Staff] were not able to fulfil such a function, and none of the senior commanders had any experience in the tactical use of the divisional formation." (Hofschroer - "Prussian Staff ..." pp 8-9)
The Convention of Paris in 1808 restricted the Prussian army to 42.000 men. In this situation the Prussians could raise not six divisions but only six brigades.
In 1812 was issued 'Exerzir-Reglement fur die Artillerie der Koniglich Preussischen Armee'. It had one section on the use of the combined arms within brigades. The brigade consisted of all arms - infantry, cavalry, artillery, engineers and staff.
When in 1813 the brigades were strenghtened with newly raised troops, and although still designated 'brigades', they were in fact 'divisions'. The regiments and brigades were well trained but iIt was apparent that the army needed more experience on multi-brigade level.
In 1813 at Dennewitz the Prussian 3rd and 4th Brigade became completely mixed up before their officers were able to put order. In 1813 at Weinberg Defile the Prussian 2nd and 7th Brigade became entangled while executing a deployment into battle formation. Despite its shorcomings the Prussian army distinguished itself at Katzbach, Dennewitz, Leipzig, and Laon. All the battles were victories. At Waterloo the Prussian army was instrumental in the ultimate defeat of Napoleon.

Prussia "... as an 'ally' of France, has been ordered to provide the French Grand Army with a 30.000-man contingent to protect its left wing, in the same way as the Austrians are to protect its right. This had caused the Berlin court to put out secret feelers to Vienna - feelers which, after three no less ruinous defeats, have fallen on deaf ears. Even so, just to make sure there are no misunderstandings, Marshal Oudinot is ordered to occupy Berlin with his 30,000-strong II Corps, while Narbonne at the same time is sent there to exercise his old-style diplomacy on a traumatized Prussian court." (Paul Britten Austin - "1812: The March on Moscow" p 27)
"The regiments mobilised for this campaign weere all (except the Leib-Regiment) 'composite' units, each consisting of infantry battalions and cavalry squadrons drawn from two parent regiments. In this way the invaluable training experience of service in the field was imparted to twice as many regiments as actually participated in the campaign. " (Digby-Smith, - p 35)
"Prussia's contribution to the French invasion of Russia was 20,842 men, grouped into 'combined regiments' drawn from all six brigades. They were commanded by Yorck, who had vociferously opposed many army reforms, with another conservative, Kleist as his second-in-command. This Corps was assigned to the left wing of the invasion, under the command of Marshal Macdonald, operating along the Baltic coast with St Petersburg as the objective. The advance bogged down around Riga, while the central army group, under Napoleon's command, disintegrated; Macdonald had to pull back before overwhelming Russian forces. During this retreat, Yorck's force became detached from the main body and surrounded. Clausewitz and Baron Stein, a former minister who had been expelled from Prussia on Napoleon's orders, open negotiations with Yorck, who finally signed the Covention of Tauroggen on December 30 1812, joining forces with the Russians and advancing with them into East Prussia." (Robert Mantle)

Charles Esdaile wrote "At Jena and Auerstadt the Prussian army had fought adequately, but its performance had hardly been heroic. At Leipzig and Waterloo, by contrast, it is claimed that a very different vision was on show.
Gunther Rothenberg writes: "In 1806 the typical Prussian soldier had been a mercenary or a reluctant conscript; now he was animated both by patriotism and by a deep and even savage hatred of the French. The first expressed itself, as it had in the days of Frederick, by religion. As the Prussian infantry saw the French retreating the evening of waterloo, the fusiliers began to sign the old Lutheran hymn, 'A mighty fortress is our God' ... Hatred of the French expressed itself in bitter fighting and in the ability to rally after initial defeat."

Prussian Army in 1813-1814.
According to Peter Hofschroer the army of 1813-14 was drawn almost entirely from the core provinces of the Kingdom of Prussia - whereas the army of 1815, consisted only in part of "old" Prussians. The Rhinelanders and to an extent the Westphalians were "new" Prussians of questionable loyalty. Also in 1815 a number of foreign, i.e. non-Prussian, formations had been amalgamated into the line and were, on paper at least, now considered regular formations, although it was really only after the Waterloo. The Rhinelanders' support for the Napoleonic code opened them up to accusations by later German nationalist historians like Treitschke of somehow being Francophile, and disloyal to the German nation. Michael Rowe writes: "The positive reception given to the codes does seem convincing evidence of Rhenish acceptance of French rule: surely it justifies locating the regiom securely within the inner empire. Yet, there is an aalternative explanation. Firstly, we need to consider what Rhinelanders liked about the Napoleonic legal system. This is not difficult, thanks to a thorough investigation conducted by the Prussian authorities after 1815. ... This revealed that the French system was popular not so much because of the contents of the civil code or penal code, but rather because of the procedures of the French courts: the oral, public proceedings in front of juries, the principle of equality before the law, and the independence of the judiciary from political interference."
By June 1813 Prussia had: 113,000 infantry, 19,000 cavalry, 16,000 artillery and 1,300 pioneers in the field. In addition to this, there were 120,500 Landwehr.
In August Prussia had:
INFANTRY
- 72,130 men in 90 infantry battalions
- 31,838 men in 39 reserve and garrison battalions
- 11,153 men in 8 jager battalions and Freikorps
- 109,120 men in 151 Landwehr battalions
CAVALRY
- 13,375 men in 89 line and national squadrons
- 3,389 men in 22 reserve squadrons
- 3,064 men in 23 jager battalions and Freikorps
- 10,952 men in 113 Landwehr squadrons
ARTILLERY
- 8,749 men in 50 field batteries
- 6,566 men in 33 fortress and siege companies

Prussian Army in 1815.
According to Barbero "At Waterloo, almost all the Prussian officers from the rank of captain up began their military service before 1806, yet the average age of the corps and divisional commanders - 45 - was the same as in Napoleon's and Wellington's...
On the eve of battle, the Prussian army was affliceted by what we call a crisis of growth.
The Congress of Vienna in 1814 had elevated the Kingdom of Prussia to the rank of a great European power, thus considerably expanding its borders and the recruitment pool at the service of its military. The human resources in the new territories, however, were thought to be less reliable than those in the old provinces of the kingdom... " (Barbero - "The Battle" p 30)

In 1815, the Prussian army consisted of:

279 infantry battalions

280 cavalry squadrons

78 artillery batteries

17 pioneer companies

1 Landwehr pioneer battalion
These forces were organized into six army corps and guard corps.
At Waterloo the Prussians had 38,000 infantry in 62 battalions, 7,000 cavalrymen in 61 squadrons, and 134 guns. Total of 50,000 men. The troops were led by seasoned officers and generals. "That the morale of the majority of the Prussian army withstood the rigours of the field and the shock of Ligny was due to the high quality of leadership at all levels. " (Adkin - "The Waterloo Companion" p 208)

After Napoleonic Wars, at the Vienna Congress, Prussia was widely perceived as under Russian influence. Prussia and Russia proposed to partition France, while Austria and England strove for and pushed through a lenient treatment of France.